Sea Lion Strandings Climb, Scientists Still Stumped

Below:

Next story in Science

Scientists still don't know why nearly 1,300 sickly sea lions
have beached themselves on the shores of southern California
since the beginning of the year. However, they think some weird
oceanic phenomenon may be blocking off the sea lion pups' source
of food, scientists reported today (April 17).

The
stranded sea lions — mostly pups born last summer — are
typically turning up alive, but severely emaciated, some weighing
less than 20 pounds (9 kg) when they should be well over 50
pounds (22 kg), marine officials say.

The National Oceanic and Atmospheric Administration (NOAA)
declared an "unusual mortality event" last month in light of the
spike in strandings. Since the beginning of the year, 1,293 sea
lions have washed ashore from San Diego County to Santa Barbara
County. That's more than five times higher than the region's
historical average of 236, averaged from the same period of time
(January through April) from 2008 to 2012, said Sarah Wilkin,
NOAA's marine mammal stranding coordinator for California.
[ Marine
Marvels: Spectacular Photos of Sea Creatures ]

The problem is most pronounced in Los Angeles County, where 459
strandings have been reported this year as of April 14. During
the same period last year, 60 strandings were reported.

California hasn't seen a spike in starving sea lions on this
scale since El Niño warmed
up Pacific waters in 1998. El Niño conditions can diminish the
upwelling of cold, nutrient-rich water needed to support large
populations of fish that are eaten by other animals like sea
lions.

"In the words of some of the other biologists, if this was an El
Niño year, it would still be overwhelming but it wouldn't be all
that surprising," Wilkin said. But this isn't an El Niño year, so
the mystery remains.

Wilkin told reporters today (April 17) that biologists think an
unseen oceanographic or environmental phenomenon is likely
cutting the sea lion pups' supply of food, much like El Niño
would. While adult sea lions and other marine mammals may be able
to adapt their feeding habits in the face of a shortage, pups are
more limited in how far they can travel for food and what they
can eat.

A localized anomaly like that happened in 2009, causing an
above-average number of strandings.

"The prevailing onshore winds did not blow as strongly as they
usually do and it resulted in a lack of upwelling, which created
a foraging difficulty for California sea lions," Wilkin
explained.

Toxic algae blooms and infectious disease outbreaks also can
trigger mass pup strandings. Researchers don't have evidence that
either of those factors are contributing to the problem this
year, but scientists are still waiting to see if tests on blood
and tissue samples turn up bacterial, viral and other infectious
agents or radioactive traces.

In a good sign, there has been a slowdown in the number of
stranded, starving sea lion pups being admitted to rehab
facilities, Wilkin said. At the same time, other animals are
washing up. Northern elephant seals have just entered their
stranding season and biologists have found a few adult female sea
lions suffering from seizures, suggesting they may have been
poisoned by the neurotoxin domoic acid, which is produced by
multiple species of the genus Pseudo-nitzschia, a type
of algae.